This invention relates generally to the field of caulking cartridges used for ejecting a caulking composition from a nozzle at a free end thereof, and more particularly to an improved plunger which is mechanically advanced by a lever on a caulking device to propel the caulking material. Devices of this general type are known in the art, and the invention relates to details of structure which provide improved operation.
Devices known in the art include a caulking cartridge which comprises a metallic tube having an ejecting nozzle at one end thereof. The tube is charged at an opposite end of caulking material following which the cartridge is closed by a movable plunger which is incrementally advanced by means on the caulking gun to eject a required amount of material through the nozzle. The initial insertion of the plunger entraps a quantity of air within the tube which must be compressed to transmit motion to the mass of caulking material. However, the air, if not released, tends to cause the upper surface of the caulking material in some areas to harden, making the advancement of the plunger difficult.
This problem has been recognized in the art. One attempted solution is the provision of small longitudinally-oriented grooves on the inner surface of the tube. This will allow atmospheric pressure to enter the tube from the free nozzle end of the cartridge, an undesirable result.
Briefly stated, the invention contemplates the provision of an improved plunger for use with a caulking tube having air venting means about the periphery thereof which is sufficiently small to permit the passage of air, but prevent the passage of caulking material therepast. This is accomplished by providing small longitudinally-oriented ribs spaced along the periphery having a width of approximately 0.020 inch, and a height of approximately 0.004 inch. Preferably the ribs are in spaced pairs providing a passage therebetween.